This invention relates to an actuator for use in the hydraulic control of a mine roof support unit.
A control system for a mine roof support assembly is known in which a respective control valve assembly is associated with each of the roof support units making up the roof support assembly. Each control valve assembly is connected, via a multi-line hydraulic hose, to an actuator having a plurality of pairs of switching valves, there being as many pairs of switching valves as there are control valves in the control valve assembly. The switching valves of each pair are detachably mounted in a pair of generally parallel bores formed in the actuator housing, and are actuable by means of a common rocker arm. By appropriate actuation of the switching valves of a given actuator, the associated control valves can be actuated to control the various operating functions of the corresponding roof support unit (for example to extend or retract the hydraulic props of that unit, or to extend or retract the hydraulic advance ram of that unit). The switching valves of a given actuator are assembled in a common actuator housing which constitutes a valve block. (see DE-OS No. 2700 829).
The aim of the invention is to provide an improved form of actuator of this type.